Study of plasmon-induced charge transfer mechanism in gold-TiO2 system is crucial and promising in the solar cell
application. To investigate charge separation and recombination dynamics in gold/TiO2 nanoparticle systems, we used
ultrafast visible-pump/IR-probe femtosecond transient absorption spectroscopy method. In our experimental study,
anatase TiO2 with different particle size 9 nm and 20 nm were chosen as electron acceptors. Plasmon-induced electron
transfer from the gold nanoparticle to the conduction band of TiO2 was studied by optical excitation of the surface
plasmon band of gold nanoparticle at 550 nm. The transient absorption kinetics were studied by probing at 3440 nm to
observe intraband free electron adsorption in TiO2. In our experimental results, electron injection was found to be
completed within the apparatus time resolution (240 fs), the charge recombination decay within 1.5 ns was
nonexponential. And when laser power changed from 0.5 μJ to 1.9 μJ, the recombination decay didn't depend on the
excitation intensity. It is interesting that we found the measured back electron transfer kinetics up to 1.5 ns were strongly
dependent on the particle size of TiO2. The plasmon-induced charge transfer mechanisms will be discussed.
The transient absorption of nanocrystalline TiO2 films in the visible-to-IR wavelength region was measured under UV
excitation conditions at different wavelengths of 266 nm and 355 nm. Under weak 355 nm excitation, the generated
charge carrier density could be reduced as low as the second-order electron-hole recombination process could be ignored
as we reported previously (Y. Tamaki et al. Phys. Chem. Chem. Phys. 9, 1453-1460 (2007)). The result was compared
with data obtained under 266 nm excitation, where the band-gap exaction was strong and efficient electron-hole
recombination occurred due to the high charge carrier density. Taking into account the dynamics of the electrons and
holes in the femtosecond to picosecond time range, such as ultrafast charge carrier trapping and slow deep trapping of
electrons, intra-band relaxation in the conduction and the valence bands and intra-particle diffusion of electrons in the
shallow trap levels were revealed.
Exciton dynamics in nanoparticles and nanotubes is important in application as well as from the fundamental point of
view. The numbers of excitons in these systems are usually very small, and fluctuations in the number are comparable to
the average number. In this situation the conventional deterministic approach that considers only the average density of
excitons is not sufficient to describe the reaction kinetics. Exciton dynamics in nanoparticles and nanotubes is analyzed on
the basis of stochastic models and compared with experiment.
Dye sensitized nanocrystalline semiconductor films are used as a photoactive part in dye-sensitized solar cells, which are recently attracting much interest both in basic and applied studies. Electron transfer reaction from a photoexcited dye molecule, which is chemically adsorbed on the surface of semiconductor, into the semiconductor conduction band is the primary step to generate photocurrent. Ultrafast pump-probe spectroscopy with a <100 fs time resolution and in a visible-to-IR wavelength range was used to elucidate the interfacial electron transfer mechanism in dye-sensitized nanocrystalline metal oxide films of ZnO, TiO2, and others. We found two types of reaction paths; one is direct electron transfer from the excited molecule to the conduction band and the other is stepwise transfer through an intermediate, which was assigned to a charge transfer complex formed by the excited molecule and a surface state on the semiconductor. The order of the observed electron transfer rates for different semiconductors was qualitatively explained by the idea of the density of electron acceptor states; that is, the larger the density of states near the energy level of the excited molecules was, the faster the electron transfer took place.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.